public class Remont
{
    [Key]
    [ForeignKey("KardOf")]
    public int RemontId { get; set; }

    [Display(Name = "Диагностика", Prompt = "Предположительно что
сломалось")]
    public List<Detal> Diagnost { get; set; }

    [Required]
    [Display(Name = "Мастер", Prompt = "Кто выполнял ремонт")]
    public Master Master { get; set; }

    public virtual Kard KardOf { get; set; }
}

public class Detal//Деталь
    {
        public int DetalId { get; set; }
        [Required]
        [Display(Name = "Деталь", Prompt = "Тип детали")]
        public string Name { get; set; }
        public List<Remont> Remonts { get; set; }
    }

[HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Diagnostic(string[] detail)
    {
        string teh = Request.Form["teh"];
        string kardId = Request.Form["kardId"];
        string master = Request.Form["master"];
        if ((teh != null) & (kardId != null) & (master != null))
        {

            ViewBag.teh = teh;
            ViewBag.kardId = kardId;
            Kard kard = db.Kards.Where(x => x.KardId.ToString() ==
kardId).FirstOrDefault();
            Master _master = db.Masters.Where(x => x.LastName ==
master).FirstOrDefault();
            if ((kard != null)&(_master != null))
            {
                Remont rem = new Remont();
                rem.Diagnost = new List<Detal>();
                //kard.Remont.
                foreach (var diag in detail)
                {
                    Detal d = db.Detals.Where(x => x.DetalId.ToString() ==
diag).FirstOrDefault();
                    if (d != null)
                    {
                        rem.Diagnost.Add(d);
                        if (d.Remonts == null) d.Remonts = new List<Remont>
();
                        d.Remonts.Add(rem);
                    }
                }

                kard.Remont = rem;
                kard.Remont.Master = _master;
                _master.RemontOf = new List<Remont>();
                _master.RemontOf.Add(kard.Remont);
                rem.KardOf = kard;

                db.Remonts.Add(kard.Remont);

                int i=db.SaveChanges();

                return RedirectToAction("Index", "Remont", new { teh =
teh});
            }
        }

        return RedirectToAction("Index", "Work");
    }

    public ActionResult Result()
    {
        string teh = Request.QueryString["teh"];
        string kardId = Request.QueryString["kardId"];
        if ((teh != null) & (kardId != null))
        {
            ViewBag.Title = "Результат ремонта";
            ViewBag.teh = teh;
            ViewBag.kardId = kardId;
            Remont result = db.Remonts.Where
                (x => x.KardOf.KardId.ToString() ==
kardId).FirstOrDefault();
            ViewBag.master_lastname = result.Master.LastName;